Currently, power supply systems that combine a solar power generation device and a storage battery exist. Such power supply systems have various arrangements made for reducing the numbers of times of charging/discharging of the storage battery.
For example, in Patent Document 1 (identified below), a deviation is obtained between a power generation amount of a solar power generation device and a power consumption amount of an AC load connected to a power system, and if the absolute value of the deviation is equal to or less than a predefined value, a switching frequency is reduced between a state of discharge from the storage battery and a state of charging of the storage battery.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2015-177647.
However, the method of Patent Document 1 takes into consideration only the deviation between the power generation amount of the solar power generation device and the power consumption amount of the AC load connected to the power system. Thus, this conventional design cannot be employed in a power supply system having a DC load connected to a DC bus line in addition to an AC load.
Moreover, in a power supply system having a DC load connected to a DC bus line, a power supply path to the DC load includes not only a path from the solar power generation device and a path from the storage battery, but also a path from the power system. Therefore, in such a power supply system, the power consumption amount of the DC load and the power consumption amount of the AC load independently affect each other, so that the method of Patent Document 1 cannot be employed.
Yet further, since the method of Patent Document 1 takes into consideration only the deviation from the power consumption amount of the AC load connected to the power system, if the absolute value of the deviation exceeds a predefined value, the storage battery is possibly discharged regardless of whether the power consumption amount of the DC load is abruptly changed. Therefore, the method has a problem of the increased numbers of times of charging/discharging of the storage battery.
Furthermore, since the storage battery is possibly discharged even when the power consumption amount of the DC load is not abruptly changed in the method of Patent Document 1, an amount of charge of the storage battery may not be sufficient so that the storage battery cannot be discharged when the power consumption amount of the DC load is abruptly changed.